Motor control device, electric power steering device, and vehicle

ABSTRACT

A motor control device includes a motor, a control device, and a motor drive circuit. The motor includes a motor rotor, a motor stator, and a plurality of coil groups divided into a first coil group and a second coil group of at least two systems for each of three phases, and configured to excite a stator core by three-phase alternating currents. In the motor drive circuit, a first motor drive circuit supplies a three-phase AC first motor drive current to the first coil group based on a command value, and a second motor drive circuit supplies a three-phase AC second motor drive current having a phase difference from a phase of the first motor drive current, to the second coil group.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Stage of PCT international applicationNo. PCT/JP2015/058329 filed on Mar. 19, 2015, which designates theUnited States, incorporated herein by reference, and which is based uponand claims the benefit of priority from Japanese Patent Application No.2014-058947 filed on Mar. 20, 2014, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a motor control device, an electricpower steering device, and a vehicle.

Description of the Related Art

A steering device motor is publicly known as a motor in which coils of astator are divided into two systems, and even if one system fails, theremaining one system can rotate a rotor. For example, Prior Art 1describes a steering device motor in which a plurality of magnetic polebodies that constitute a stator are divided into two groups including asystem A group and a system B group. In Prior Art 1, the system Aincludes a system A-1 including a plurality of magnetic pole bodiescontinuously arranged and a system A-2 including a plurality of magneticpole bodies arranged in a state of facing the magnetic pole bodiesbelonging to the system A-1 in a diameter direction. The same applies tothe system B.

CITATION LIST Prior Art

Prior Art 1: Japanese Laid-open Patent Publication No. 2007-331639

In the steering device motor described in Prior Art 1, if the system Bgroup of the two groups fails, the motor is driven only by the system Agroup. However, since the system A-1 and the system A-2 are arranged toface each other in the diameter direction, variation in positions wheretorque is generated in a circumferential direction becomes large.

The present invention has been made in view of the above, and isdirected to providing a motor control device, an electric power steeringdevice, and a vehicle that can suppress torque ripple when coil groupsof at least two systems excited independently of each other are excitedat the same time.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problems and achieve the purpose,there is provided a motor control device comprising: a motor including:a motor rotor; a motor stator including a stator core that rotates themotor rotor; and a plurality of coil groups divided into a first coilgroup and a second coil group of at least two systems for each of threephases, and configured to excite the stator core by three-phasealternating currents; and a motor drive circuit including: a controldevice that outputs a current value as a command value for rotating anddriving the motor rotor; a first motor drive circuit that supplies athree-phase AC first motor drive current to the first coil group, basedon the command value; and a second motor drive circuit that supplies athree-phase AC second motor drive current having a phase difference froma phase of the first motor drive current, to the second coil group.

With the above-described configuration, the motor control device cansuppress the torque ripple when the two coil groups of at least twosystems excited independently of each other are excited at the sametime.

According to a preferred aspect, it is preferable that the controldevice includes: a control unit that calculates a pulse width modulationsignal with a predetermined duty ratio as the command value; and a phasedifference adjusting unit that calculates a second pulse widthmodulation signal from a first pulse width modulation signal that is thepulse width modulation signal with the predetermined duty ratio, suchthat the second pulse width modulation signal has the same duty ratio asthe first pulse width modulation signal, and has a phase difference fromthe first pulse width modulation signal.

With the above-described configuration, the phase difference adjustingunit of the control device can adjust the phase difference in a rangewhere the decreasing rate of torque ripple is larger than the decreasingrate of average torque, and the motor can perform control to providerotation with decreased torque ripple to the motor rotor. Further, thephase difference adjusting unit can perform control to approximate thephase difference to 0 to increase the average torque, and increase thephase difference to decrease the torque ripple.

According to a preferred aspect, it is preferable that the first motordrive circuit supplies the first motor drive current to the first coilgroup by PWM control of the first pulse width modulation signal, and thesecond motor drive circuit supplies the second motor drive current tothe second coil group by PWM control of the second pulse widthmodulation signal.

With the above-described configuration, the first motor drive circuitand the second motor drive circuit that are independent from each otherare provided, whereby redundancy is enhanced, and fail safety of themotor drive circuit can be enhanced.

According to a preferred aspect, it is preferable that the phasedifference does not exceed 45° in electrical angle. Accordingly, adecrease in the average torque can be suppressed.

According to a preferred aspect, it is preferable to provide an electricpower steering device configured to obtain auxiliary steering torque bythe motor of the above-described motor control device. With thisstructure, the torque ripple can be suppressed when the coil groups ofat least two systems excited independently of each other are excited atthe same time. Therefore, the electric power steering device lowers apossibility of causing an operator to feel vibration due to the torqueripple, and making the operator uncomfortable. Therefore, the electricpower steering device can allow a steerer to operate a vehicle whilepreventing the steerer from feeling uncomfortable. As a result, theelectric power steering device can provide comfortable steering feelingto the operator.

According to a preferred aspect, it is preferable to provide a vehicleon which the above-described electric power steering device is mounted.

According to the present invention, it is possible to provide a motorcontrol device, an electric power steering device, and a vehicle thatsuppress torque ripple when coil groups of at least two systems excitedindependently of each other are excited at the same time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an electric power steering deviceincluding a motor according to a first embodiment.

FIG. 2 is a front view for explaining an example of a reduction gearincluded in the electric power steering device of the first embodiment.

FIG. 3 is a sectional view schematically illustrating a configuration ofthe motor of the first embodiment by cutting the motor in a virtualplane including a central axis.

FIG. 4 is a sectional view schematically illustrating a configuration ofthe motor of the first embodiment by cutting the motor in a virtualplane perpendicular to the central axis.

FIG. 5 is a schematic diagram for explaining drive of the motor by anECU.

FIG. 6 is a schematic diagram illustrating wires of first coils andwires of second coils.

FIG. 7 is a schematic diagram illustrating wires of first coils andwires of second coils according to a first modification.

FIG. 8 is a sectional view schematically illustrating a configuration ofa motor according to a second modification by cutting the motor in avirtual plane perpendicular to a central axis.

FIG. 9 is a sectional view schematically illustrating a configuration ofa motor according to a third modification by cutting the motor in avirtual plane perpendicular to a central axis.

FIG. 10 is a diagram for explaining waveforms of first U-phase andsecond U-phase currents to be supplied to a motor according to thesecond embodiment.

FIG. 11 is a diagram for explaining change amounts of average torque andtorque ripple with respect to a phase difference between a phase of afirst motor drive current and a phase of a second motor drive current.

FIG. 12 is a diagram illustrating vector relationships between anarmature magnetic flux of first coil groups and an armature magneticflux of second coil groups in a d axis and a q axis.

FIG. 13 is a schematic diagram of a vehicle on which the electric powersteering device including the motor according to the first or secondembodiment is mounted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Modes (embodiments) for implementing the present invention will bedescribed in detail with reference to the drawings. The presentinvention is not limited by content described in the embodiments. Theconfiguration elements described below include those easily conceived bya person skilled in the art and those substantially the same. Further,the configuration elements described below can be appropriatelycombined.

First Embodiment Electric Power Steering Device

FIG. 1 is a configuration diagram of an electric power steering deviceincluding a motor according to a first embodiment. In the firstembodiment, an outline of an electric power steering device 80 includinga motor 10 will be described with reference to FIG. 1.

The electric power steering device 80 includes, in transmission order offorce supplied from a steerer, a steering wheel 81, a steering shaft 82,a steering force assist mechanism 83, a universal joint 84, a lowershaft 85, a universal joint 86, a pinion shaft 87, a steering gear 88,and a tie rod 89. Further, the electric power steering device 80includes an ECU (Electronic Control Unit) 90, a torque sensor 91 a, anda vehicle speed sensor 91 b.

The steering shaft 82 includes an input shaft 82 a and an output shaft82 b. The input shaft 82 a has one end portion coupled with the steeringwheel 81, and the other end portion coupled with the steering forceassist mechanism 83 through the torque sensor 91 a. The output shaft 82b has one end portion coupled with the steering force assist mechanism83, and the other end portion coupled with the universal joint 84. Inthe first embodiment, the input shaft 82 a and the output shaft 82 b areformed of a magnetic material such as iron.

The lower shaft 85 has one end portion coupled with the universal joint84, and the other end portion coupled with the universal joint 86. Thepinion shaft 87 has one end portion coupled with the universal joint 86,and the other end portion coupled with the steering gear 88.

The steering gear 88 includes a pinion 88 a and a rack 88 b. The pinion88 a is coupled with the pinion shaft 87. The rack 88 b is meshed withthe pinion 88 a. The steering gear 88 is configured as a rack and pinionsystem. The steering gear 88 converts rotary movement transmitted to thepinion 88 a into translatory movement in the rack 88 b. The tie rod 89is coupled with the rack 88 b.

The steering force assist mechanism 83 includes a reduction gear 92 anda motor 10. The reduction gear 92 is coupled with the output shaft 82 b.The motor 10 is a motor that is coupled with the reduction gear 92 andthat generates auxiliary steering torque. A steering column of theelectric power steering device 80 is constituted of the steering shaft82, the torque sensor 91 a, and the reduction gear 92. The motor 10provides the auxiliary steering torque to the output shaft 82 b of thesteering column. That is, the electric power steering device 80 of thefirst embodiment employs a column assist system.

In the electric power steering device 80 in the column assist system,the distance between an operator and the motor 10 is relatively short,and torque change or friction force of the motor 10 may affect thesteerer. Therefore, the electric power steering device 80 is required todecrease the friction force of the motor 10.

FIG. 2 is a front view for explaining an example of the reduction gearincluded in the electric power steering device of the first embodiment.A part of FIG. 2 is illustrated as a cross section. The reduction gear92 is a worm reduction gear. The reduction gear 92 includes a reductiongear housing 93, a worm 94, a ball bearing 95 a, a ball bearing 95 b, aworm wheel 96, and a holder 97.

The worm 94 is coupled with a shaft 21 of the motor 10 through a splinecoupling or an elastic coupling. The worm 94 is rotatably held in thereduction gear housing 93 by the ball bearing 95 a and the ball bearing95 b that is held in the holder 97. The worm wheel 96 is rotatably heldin the reduction gear housing 93. Worm teeth 94 a formed in a part ofthe worm 94 are meshed with worm wheel teeth 96 a formed in the wormwheel 96.

Rotating force of the motor 10 is transmitted to the worm wheel 96through the worm 94, which rotates the worm wheel 96. The reduction gear92 increases the torque of the motor 10 by the worm 94 and the wormwheel 96. The reduction gear 92 then provides the auxiliary steeringtorque to the output shaft 82 b of the steering column illustrated inFIG. 1.

The torque sensor 91 a illustrated in FIG. 1 detects steering force of adriver, which has been transmitted to the input shaft 82 a through thesteering wheel 81, as steering torque. The vehicle speed sensor 91 bdetects travel speed of a vehicle on which the electric power steeringdevice 80 is mounted. The motor 10, the torque sensor 91 a, and thevehicle speed sensor 91 b are electrically connected to the ECU 90.

The ECU 90 controls an operation of the motor 10. Further, the ECU 90acquires signals each from the torque sensor 91 a and the vehicle speedsensor 91 b. That is, the ECU 90 acquires steering torque T from thetorque sensor 91 a, and acquires travel speed V of the vehicle from thevehicle speed sensor 91 b. The ECU 90 is supplied with power from apower supply device (for example, an in-vehicle battery) 99 when anignition switch 98 is in an ON-state. The ECU 90 calculates an auxiliarysteering command value of an assist command based on the steering torqueT and the travel speed V. The ECU 90 then adjusts a power value X to besupplied to the motor 10, based on the calculated auxiliary steeringcommand value. The ECU 90 acquires information of an induced voltagefrom the motor 10 or information of rotation of a rotor from a resolverto be described below, as operation information Y.

The steering force of the steerer (driver) input to the steering wheel81 is transmitted to the reduction gear 92 of the steering force assistmechanism 83 through the input shaft 82 a. At this time, the ECU 90acquires the steering torque T input to the input shaft 82 a from thetorque sensor 91 a, and acquires the travel speed V from the vehiclespeed sensor 91 b. The ECU 90 then controls an operation of the motor10. The auxiliary steering torque produced by the motor 10 istransmitted to the reduction gear 92.

The steering torque T (including the auxiliary steering torque) outputthrough the output shaft 82 b is transmitted to the lower shaft 85through the universal joint 84, and is further transmitted to the pinionshaft 87 through the universal joint 86. The steering force transmittedto the pinion shaft 87 is transmitted to the tie rod 89 through thesteering gear 88, which steers a steering wheel. Next, the motor 10 willbe described.

(Motor)

FIG. 3 is a sectional view schematically illustrating a configuration ofthe motor of the first embodiment by cutting the motor in a virtualplane including a central axis. FIG. 4 is a sectional view schematicallyillustrating a configuration of the motor of the first embodiment bycutting the motor in a virtual plane perpendicular to the central axis.As illustrated in FIG. 3, the motor 10 includes a housing 11, a bearing12, a bearing 13, a resolver 14, a motor rotor 20, and a motor stator 30for a blushless motor.

The housing 11 includes a cylindrical housing 11 a and a front bracket11 b. The front bracket 11 b is formed in a substantially disk shape,and is attached to the cylindrical housing 11 a so as to block oneopening end portion of the cylindrical housing 11 a. The cylindricalhousing 11 a has a bottom 11 c formed so as to block an end portion atthe opposite side of the front bracket 11 b. The bottom 11 c isintegrally formed with the cylindrical housing 11 a, for example. As amaterial forming the cylindrical housing 11 a, for example, a typicalsteel material such as steel plate cold commercial (SPCC),electromagnetic soft iron, and aluminum can be employed. Further, thefront bracket 11 b serves as a flange when the motor 10 is attached to adesired device.

The bearing 12 is provided inside the cylindrical housing 11 a, and at asubstantially central portion of the front bracket 11 b. The bearing 13is provided inside the cylindrical housing 11 a, and at a substantiallycentral portion of the bottom 11 c. The bearing 12 rotatably supportsone end of the shaft 21 that is a part of the motor rotor 20 arrangedinside the cylindrical housing 11 a. The bearing 13 rotatably supportsthe other end of the shaft 21. Accordingly, the shaft 21 rotates aroundan axis as a rotation center Zr.

The resolver 14 is supported by a terminal table 15 provided at thefront bracket 11 b side of the shaft 21. The resolver 14 detects arotation position of the motor rotor 20 (shaft 21). The resolver 14includes a resolver rotor 14 a and a resolver stator 14 b. The resolverrotor 14 a is attached to a circumferential surface of the shaft 21 bymeans of press-fitting or the like. The resolver stator 14 b is arrangedto face the resolver rotor 14 a with a gap having a predeterminedinterval.

The motor rotor 20 is provided inside the cylindrical housing 11 a sothat the motor rotor 20 can rotate around the rotation center Zr withrespect to the cylindrical housing 11 a. The motor rotor 20 includes theshaft 21, a rotor yoke 22, and a magnet 23. The shaft 21 is formed in acylindrical manner. The rotor yoke 22 is formed in a cylindrical manner.The rotor yoke 22 has an arc-shaped outer circumference. Theconfiguration reduces machining man-hours for a punching processcompared to a case where the outer circumference has a complicatedshape.

The rotor yoke 22 is manufactured by laminating sheets such as anelectrical steel sheet and a cold rolled steel sheet by means ofbonding, a boss, or caulking. The rotor yoke 22 is formed bysequentially laminating sheets in a mold and is discharged from themold. The rotor yoke 22 is fixed to the shaft 21 by press-fitting theshaft 21 into a hollow portion of the rotor yoke 22, for example. Theshaft 21 and the rotor yoke 22 may be integrally formed.

The magnet 23 is fixed on a surface of the rotor yoke 22 along acircumferential direction of the rotor yoke 22, and a plurality ofmagnets 23 are provided. The magnets 23 are permanent magnets, and Spoles and N poles are alternately arranged in the circumferentialdirection of the rotor yoke 22 at regular intervals. Accordingly, the Npoles and the S poles are alternately arranged on an outercircumferential side of the rotor yoke 22 in the circumferentialdirection of the rotor yoke 22, and the number of poles of the motorrotors 20 illustrated in FIG. 4 is eight.

The motor stator 30 is provided in a cylindrical manner to surround themotor rotor 20 inside the cylindrical housing 11 a. The motor stator 30is fitted into an inner circumferential surface 11 d of the cylindricalhousing 11 a, for example, so that the motor stator 30 is attachedthereto. A central axis of the motor stator 30 coincides with therotation center Zr of the motor rotor 20. The motor stator 30 includes acylindrical stator core 31, a plurality of first coils 37, and aplurality of second coils 38.

As illustrated in FIG. 4, the stator core 31 includes an annular backyoke 33, and a plurality of teeth 34 arranged side by side in acircumferential direction around the rotation center Zr on an innercircumferential surface of the back yoke 33. In the description below,the circumferential direction around the rotation center Zr(circumferential direction of the stator core 31) is simply described asthe circumferential direction. The stator core 31 is formed of amagnetic material such as electrical steel. The stator core 31 is formedsuch that a plurality of core pieces formed in the substantially sameshape are laminated and bundled in an axial direction parallel to theaxis of the rotation center Zr. The back yoke 33 is, for example, acylindrical member. The teeth 34 protrude from the inner circumferentialsurface of the back yoke 33. In the first embodiment, the twelve teeth34 are arranged in the circumferential direction. The tooth 34 includesa tooth tip 32 at a top portion opposite to the back yoke 33. The toothtip 32 protrudes from the tooth 34 in the circumferential direction. Theteeth 34 face an outer circumferential surface of the rotor yoke 22. Thestator core 31 is annularly arranged outside the rotor yoke 22 in aradial direction with a predetermined interval.

The stator core 31 is press-fitted into the cylindrical housing 11 a, sothat the motor stator 30 is provided inside the cylindrical housing 11 ain an annular state. The stator core 31 and the cylindrical housing 11 amay be fixed to each other by means of bonding, shrink-fitting, orwelding, other than the press-fitting.

As illustrated in FIG. 4, the first coils 37 are respectively woundaround the teeth 34 in a concentrated manner. The first coil 37 is woundaround an outer circumference of the tooth 34 in a concentrated mannerthrough an insulator 37 a (refer to FIG. 3). The insulator 37 a is amember for insulating the first coil 37 and the stator core 31 from eachother, and is formed of a heat resistant member. All of the first coils37 are included in a first coil system that is excited by the sameinverter (a first inverter 52 described below). In the first embodiment,the first coil system includes six first coils 37, for example. The sixfirst coils 37 are arranged such that two first coils 37 are adjacent toeach other in the circumferential direction. Three first coil groups G1,each including the adjacent two first coils 37 as one group, arearranged in the circumferential direction at regular intervals. That is,the first coil system includes the three first coil groups G1 arrangedin the circumferential direction at regular intervals. The number of thefirst coil groups G1 is not necessarily three, and may be 3n where n isan integer, i.e., 3n first coil groups G1 are arranged in thecircumferential direction at regular intervals. In addition, n isdesirably an odd number.

As illustrated in FIG. 4, the second coils 38 are respectively woundaround a plurality of teeth 34 in a concentrated manner. The second coil38 is wound around an outer circumference of the tooth 34 through aninsulator in a concentrated manner. The teeth 34 around which the secondcoils 38 are wound in a concentrated manner are different from the teeth34 around which the first coils 37 are wound in a concentrated manner.All of the second coils 38 are included in a second coil system that isexcited by the same inverter (a second inverter 54 described below). Inthe first embodiment, the second coil system includes six second coils38, for example. The six second coils 38 are arranged such that twosecond coils 38 are adjacent to each other in the circumferentialdirection. Three second coil groups G2, each including the adjacent twosecond coils 38 as one group, are arranged in the circumferentialdirection at regular intervals. That is, the second coil system includesthree second coil groups G2 arranged in the circumferential direction atregular intervals. The number of the second coil groups G2 is notnecessarily three, and may be 3n where n is an integer, i.e., 3n secondcoil groups G2 are arranged in the circumferential direction at regularintervals where n is an integer. In addition, n is desirably an oddnumber.

FIG. 5 is a schematic diagram for explaining drive of the motor by theECU. A motor control device 100 includes the ECU 90 and the motor 10.The motor control device 100 can input an input signal from a sensorsuch as the torque sensor 91 a to the ECU 90, for example. The ECU 90controls the operation of the motor 10 by three-phase alternatingcurrents. The ECU 90 includes a control device 40 that controls themotor 10 and a motor drive circuit 50. The control device 40 outputs acurrent value as a command value for rotating and driving the motorrotor 20. The motor drive circuit 50 is a power supply circuit thatgenerates a pulse width modulation signal with a predetermined dutyratio, which is called PWM (Pulse Width Modulation), based on thecommand value of the control device 40, and that outputs a three-phasealternating current signal for controlling a current value of the motor10. The motor drive circuit 50 only needs to be electrically connectedwith the control device 40, and is installed at a position differentfrom a position where the control device 40 is installed, to suppress aninfluence of heat generated in the motor drive circuit 50.

The control device 40 includes a control unit 40A and a phase differenceadjusting unit 40B. The control unit 40A includes, as function blocks, amain control unit 41, a first coil system control unit 42, and a secondcoil system control unit 44. The phase difference adjusting unit 40Bincludes, as function blocks, a first phase adjusting unit 43 and asecond phase adjusting unit 45.

The motor drive circuit 50 includes a first motor drive circuit 50A anda second motor drive circuit 50B. The first motor drive circuit 50Asupplies a three-phase AC first motor drive current to the first coilgroups G1 based on the command value. The second motor drive circuit 50Bsupplies a three-phase AC second motor drive current to the second coilgroups G2. The first motor drive circuit 50A includes a first gate drivecircuit 51 and a first inverter 52. The second motor drive circuit 50Bincludes a second gate drive circuit 53 and a second inverter 54.

The main control unit 41 acquires the steering torque T input to theinput shaft 82 a from the torque sensor 91 a. The main control unit 41calculates a current value as a command value for rotating and drivingthe motor rotor 20 according to the information acquired from the torquesensor 91 a. The first coil system control unit 42 calculates a firstpulse width modulation signal with a predetermined duty ratio, based onthe command value of the main control unit 41. The first coil systemcontrol unit 42 transmits information of the first pulse widthmodulation signal to the first phase adjusting unit 43. The second coilsystem control unit 44 calculates a second pulse width modulation signalwith a predetermined duty ratio, based on the command value of the maincontrol unit 41. The second coil system control unit 44 transmitsinformation of the second pulse width modulation signal to the secondphase adjusting unit 45. In the first embodiment, the first phaseadjusting unit 43 and the second phase adjusting unit 45 adjust a phaseof a current to be supplied to the first coil groups G1 and a phase of acurrent to be supplied to the second coil groups G2 to become the same.At the time when the first coil system control unit 42 and the secondcoil system control unit 44 output the signals, if there is no phasedifference between the information of the first pulse width modulationsignal and the information of the second pulse width modulation signal,and these signals are synchronized with each other, the phase differenceadjusting unit 40B may not be provided. The first phase adjusting unit43 transmits information of the adjusted first pulse width modulationsignal to the first gate drive circuit 51. The second phase adjustingunit 45 transmits information of the adjusted second pulse widthmodulation signal to the second gate drive circuit 53.

The first gate drive circuit 51 controls the first inverter 52 based onthe information of the first pulse width modulation signal acquired fromthe first phase adjusting unit 43. The first inverter 52 switches afield effect transistor on and off to generate the three-phasealternating currents including a first U phase, a first V phase, and afirst W phase, and having three-phase current values according to theduty ratio of the first pulse width modulation signal in the first gatedrive circuit 51. The three-phase alternating currents generated by thefirst inverter 52 are sent to the motor 10 through three wires Lu1, Lv1,and Lw1, and excite the first coils 37. The wire Lu1 sends a firstU-phase current to the motor 10. The wire Lv1 sends a first V-phasecurrent to the motor 10. The wire Lw1 sends a first W-phase current tothe motor 10.

The second gate drive circuit 53 controls the second inverter 54 basedon the information of the second pulse width modulation signal acquiredfrom the second phase adjusting unit 45. The second inverter 54 switchesa field effect transistor on and off to generate the three-phasealternating currents including a second U phase, a second V phase, and asecond W phase, and having three-phase current values according to theduty ratio of the second pulse width modulation signal in the secondgate drive circuit 53. The three-phase alternating currents generated bythe second inverter 54 are sent to the motor 10 through three wires Lu2,Lv2, and Lw2, and excite the second coils 38. The wire Lu2 sends asecond U-phase current to the motor 10. The wire Lv2 sends a secondV-phase current to the motor 10. The wire Lw2 sends a second W-phasecurrent to the motor 10.

As described above, the control device 40 supplies the first pulse widthmodulation signal and the second pulse width modulation signal with apredetermined duty ratio, which serve as the current values fordesirably rotating and driving the motor rotor 20, to the first gatedrive circuit 51 and the second gate drive circuit 53, therebycontrolling the first motor drive circuit 50A and the second motor drivecircuit 50B.

FIG. 6 is a schematic diagram illustrating the wires of the first coilsand the second coils. As illustrated in FIG. 6, the six first coils 37include two first U-phase coils 37Ua and 37Ub that are excited by thefirst U-phase current, two first V-phase coils 37Va and 37Vb that areexcited by the first V-phase current, and two first W-phase coils 37Waand 37Wb that are excited by the first W-phase current. The firstU-phase coil 37Ub is connected with the first U-phase coil 37Ua inseries. The first V-phase coil 37Vb is connected with the first V-phasecoil 37Va in series. The first W-phase coil 37Wb is connected with thefirst W-phase coil 37Wa in series. All of the first coils 37 are woundaround the teeth 34 in the same winding direction. Further, the wiresLu1, Lv1, and Lw1 are connected by Y-connection.

As illustrated in FIG. 6, the six second coils 38 include two secondU-phase coils 38Ua and 38Ub that are excited by the second U-phasecurrent, two second V-phase coils 38Va and 38Vb that are excited by thesecond V-phase current, and two second W-phase coils 38Wa and 38Wb thatare excited by the second W-phase current. The second U-phase coil 38Ubis connected with the second U-phase coil 38Ua in series. The secondV-phase coil 38Vb is connected with the second V-phase coil 38Va inseries. The second W-phase coil 38Wb is connected with the secondW-phase coil 38Wa in series. All of the second coils 38 are wound aroundthe teeth 34 in the same winding direction, which is the same as thewinding direction of the first coils 37. Further, the wires Lu2, Lv2,and Lw2 are connected by Y-connection.

As illustrated in FIG. 6, the motor of the first embodiment thatincludes the Y-connected six first coils 37 and the Y-connected sixsecond coils 38 has been exemplarily described. However, a motorincluding A-connected six first coils 37 and A-connected six secondcoils 38 may be employed.

As illustrated in FIG. 4, the three first coil groups G1 are constitutedof a first UV coil group G1UV, a first VW coil group G1VW, and a firstUW coil group G1UW. The first UV coil group G1UV includes the firstU-phase coil 37Ub and the first V-phase coil 37Va adjacent to each otherin the circumferential direction. The first VW coil group G1VW includesthe first V-phase coil 37Vb and the first W-phase coil 37Wa adjacent toeach other in the circumferential direction. The first UW coil groupG1UW includes the first U-phase coil 37Ua and the first W-phase coil37Wb adjacent to each other in the circumferential direction.

As illustrated in FIG. 4, the three second coil groups G2 areconstituted of a second UV coil group G2UV, a second VW coil group G2VW,and a second UW coil group G2UW. The second UV coil group G2UV includesthe second U-phase coil 38Ub and the second V-phase coil 38Va adjacentto each other in the circumferential direction. The second VW coil groupG2VW includes the second V-phase coil 38Vb and the second W-phase coil38Wa adjacent to each other in the circumferential direction. The secondUW coil group G2UW includes the second U-phase coil 38Ua and the secondW-phase coil 38Wb adjacent to each other in the circumferentialdirection.

The first coils 37 that are excited by the first U-phase current facethe second coils 38 that are excited by the second U-phase current inthe radial direction of the stator core 31. In the description below,the radial direction of the stator core 31 is simply described as theradial direction. For example, as illustrated in FIG. 4, the firstU-phase coil 37Ua faces the second U-phase coil 38Ua in the radialdirection, and the first U-phase coil 37Ub faces the second U-phase coil38Ub in the radial direction.

The first coils 37 that are excited by the first V-phase current facethe second coils 38 that are excited by the second V-phase current inthe radial direction. For example, as illustrated in FIG. 4, the firstV-phase coil 37Va faces the second V-phase coil 38Va in the radialdirection, and the first V-phase coil 37Vb faces the second V-phase coil38Vb in the radial direction.

The first coils 37 that are excited by the first W-phase current facethe second coils 38 that are excited by the second W-phase current inthe radial direction. For example, as illustrated in FIG. 4, the firstW-phase coil 37Wa faces the second W-phase coil 38Wa in the radialdirection, and the first W-phase coil 37Wb faces the second W-phase coil38Wb in the radial direction.

As described above, the first coils 37 are excited by the first inverter52, and the second coils 38 are excited by the second inverter 54.Accordingly, the first inverter 52 and the second inverter 54 supply thethree-phase alternating currents to the motor 10 independently of eachother. Therefore, even if it becomes impossible to supply a current tothe second coils 38, the first coils 37 can drive the motor 10. Further,even if it becomes impossible to supply a current to the first coils 37,the second coils 38 can drive the motor 10. The following describes anexemplary case where it becomes impossible to supply a current to thesecond coils 38. Description of a case where it becomes impossible tosupply a current to the first coils 37 is the same as the case of thesecond coils 38 and thus will not be repeated.

Further, the three first coil groups G1 each constituted of the firstcoils 37 are arranged in the circumferential direction at regularintervals. Accordingly, the distance between the first coil groups G1 inthe circumferential direction becomes shorter than a case where twofirst coil groups G1 are arranged in the circumferential direction atregular intervals. Therefore, even if it becomes impossible to supply acurrent to the second coils 38, variation of positions in thecircumferential direction where the first coils 37 generate torquebecomes small. Therefore, the motor 10 can suppress an increase intorque ripple even in the case of drive only by one of the two coilsystems that are excited independently of each other.

Further, the three first coil groups G1 are constituted of the first UVcoil group G1UV, the first VW coil group G1VW, and the first UW coilgroup G1UW. The second coil groups G2 are constituted of the second UVcoil group G2UV, the second VW coil group G2VW, and the second UW coilgroup G2UW. Accordingly, two first coils 37 excited by the same-phasecurrent do not belong to one first coil group G1, and two second coils38 excited by the same phase current do not belong to one second coilgroup G2. The two first coils 37 excited by the same phase currentindicate any of the two first U-phase coils 37Ua and 37Ub, the two firstV-phase coils 37Va and 37Vb, and the two first W-phase coils 37Wa and37Wb. Therefore, positions where the torque is generated tend to bedispersed in the circumferential direction. Therefore, the motor 10 canfurther suppress the torque tipple.

In the case of using the technology of Prior Art 1, when the motor isdriven by one of the two systems, coils arranged at an end portion inthe circumferential direction of the system are those excited byspecific two phases (any of the combinations of a U phase and a V phase,a V phase and a W phase, and a U phase and a W phase). Accordingly, ageneration amount of torque tends to vary according to change of thephases of the three-phase alternating currents, and thus the torqueripple may be increased. On the other hand, in the motor 10 according tothe first embodiment, the first U-phase coils 37Ua and 37Ub, the firstV-phase coils 37Va and 37Vb, or the first W-phase coils 37Wa and 37Wbare arranged at an end portion of the first coil groups G1 in thecircumferential direction. The second U-phase coils 38Ua and 38Ub, thesecond V-phase coils 38Va and 38Vb, or the second W-phase coils 38Wa and38Wb are arranged at an end portion of the second coil groups G2 in thecircumferential direction. Accordingly, in the motor 10, the generationamount of the torque hardly varies according to change of the phases ofthe three-phase alternating currents. Therefore, an increase in thetorque ripple can be further suppressed.

The column assist system of the electric power steering device 80 of thefirst embodiment has been exemplarily described. However, a pinionassist system and a rack assist system can also be employed.

As described above, the motor 10 is provided with the annular statorcore 31 including the annular back yoke 33 and the teeth 34 arrangedside by side in the circumferential direction on the innercircumferential surface of the back yoke 33. The motor 10 includes the3n first coil groups G1 (three in the first embodiment) that arearranged in the circumferential direction of the stator core 31 atregular intervals, where n is an integer. Each of the first coil groupsG1 is constituted of the first coils 37 (two in the first embodiment)that are respectively wound in a concentrated manner around the teeth 34(two in the first embodiment) that are arranged adjacent to each otherand excited by the first inverter 52 configured to generate thethree-phase alternating currents including the first U phase, the firstV phase, and the first W phase. The motor 10 includes the 3n second coilgroups G2 (three in the first embodiment) that are arranged in thecircumferential direction of the stator core 31 at regular intervals.Each of the second coil groups G2 is constituted of the second coils 38(two in the first embodiment) that are respectively wound in aconcentrated manner around the teeth 34 (two in the first embodiment)that are arranged adjacent to each other at positions, different frompositions of the teeth 34 around which the first coils 37 are wound in aconcentrated manner, and that are excited by the second inverter 54configured to generate the three-phase alternating currents includingthe second U phase, the second V phase, and the second W phase.

Accordingly, the distance between the first coil groups G1 in thecircumferential direction becomes shorter than the case where two firstcoil groups G1 are arranged in the circumferential direction at regularintervals. Therefore, even if it becomes impossible to supply a currentto the second coils 38, variation of the positions where the first coils37 generate the torque in the circumferential direction becomes small.Therefore, the motor 10 can suppress an increase in torque ripple, evenin the case of drive by only one of the two coil systems that areexcited independently of each other.

Further, the first coils 37 (six in the first embodiment) include thefirst U-phase coils 37Ua and 37Ub (two in the first embodiment) that areexcited by the first U-phase current, the first V-phase coils 37Va and37Vb (two in the first embodiment) that are excited by the first V-phasecurrent, and the first W-phase coils 37Wa and 37Wb (two in the firstembodiment) that are excited by the first W-phase current. The secondcoils 38 (six in the first embodiment) include the second U-phase coils38Ua and 38Ub (two in the first embodiment) that are excited by thesecond U-phase current, the second V-phase coils 38Va and 38Vb (two inthe first embodiment) that are excited by the second V-phase current,and the second W-phase coils 38Wa and 38Wb (two in the first embodiment)that are excited by the second W-phase current. The 3n first coil groupsG1 (three in the first embodiment) are constituted of the first UV coilgroup G1UV including the first U-phase coil 37Ub and the first V-phasecoil 37Va, the first VW coil group G1VW including the first V-phase coil37Vb and the first W-phase coil 37Wa, and the first UW coil group G1UWincluding the first U-phase coil 37Ua and the first W-phase coil 37Wb.The 3n second coil groups G2 (three in the first embodiment) include thesecond UV coil group G2UV including the second U-phase coil 38Ub and thesecond V-phase coil 38Va, the second VW coil group G2VW including thesecond V-phase coil 38Vb and the second W-phase coil 38Wa, and thesecond UW coil group G2UW including the second U-phase coil 38Ua and thesecond W-phase coil 38Wb.

Accordingly, two first coils 37 excited by the same phase current do notbelong to one first coil group G1, and two second coils 38 excited bythe same phase current do not belong to one second coil group G2.Therefore, positions where the torque is generated tend to be dispersedin the circumferential direction. Therefore, the motor 10 can furthersuppress the torque ripple.

(First Modification)

FIG. 7 is a schematic diagram illustrating wires of first coils andwires of second coils according to a first modification. The sameconfiguration elements as those described in the first embodiment aredenoted with the same reference signs, and overlapping description isomitted.

In a motor 10 according to the first modification, a winding directionin which second coils 38 are wound around teeth 34 is opposite to awinding direction in which first coils 37 are wound around teeth 34.Further, in the motor 10 according to the first modification, a firstphase adjusting unit 43 and a second phase adjusting unit 45 adjust aphase of a current to be supplied to a first coil group G1 and a phaseof a current to be supplied to a second coil group G2 to becomedifferent from each other by 180°. Accordingly, directions of magneticfields generated by the first coils 37 and the second coils 38 becomethe same as those of the first embodiment.

Since the winding direction in which the second coils 38 are woundaround the teeth 34 are opposite to the winding direction in which thefirst coils 37 are wound around the teeth 34, a position to startwinding the first coils 37 around the teeth 34 is different from aposition to start winding the second coils 38 around the teeth 34. Forexample, if the first coils 37 are started to be wound around the teeth34 from an outside end portion of the teeth 34 in the radial direction,the second coils 38 are started to be wound around the teeth 34 from aninside end portion of the teeth 34 in the radial direction. Therefore,as illustrated in FIG. 7, end portions of the wires Lu1, Lv1, and Lw1,at a side connected to the first inverter 52, are positioned closer tothe outside of the motor 10 in the radial direction, and end portions ofthe wires Lu2, Lv2, and Lw2, at a side connected to the second inverter54, are positioned closer to the inside of the motor 10 in the radialdirection. Therefore, positions of the wires connected to the motor 10tend to vary. Therefore, the motor 10 according to the firstmodification can reduce a possibility of mutual interference among thewires.

Further, the phase of the current to be supplied to the first coilgroups G1 and the phase of the current to be supplied to the second coilgroups G2 are different from each other by 180°. Therefore, radiationnoise from the wires Lu1, Lv1, and Lw1 between the first inverter 52 andthe motor 10 and radiation noise from the wires Lu2, Lv2, and Lw2between the second inverter 54 and the motor 10 offset each other.Therefore, the radiation noise generated in the wires between an ECU 90and the motor 10 are reduced.

(Second Modification)

FIG. 8 is a sectional view schematically illustrating a configuration ofa motor according to a second modification by cutting the motor in avirtual plane perpendicular to a central axis. As illustrated in FIG. 8,N poles and S poles are alternately arranged on an outer circumferentialside of a rotor yoke 22 in a circumferential direction of the rotor yoke22, and the number of poles of a motor rotor 20 in the secondmodification is 20. Further, twenty-four teeth 34 are arranged in thecircumferential direction.

As illustrated in FIG. 8, in the second modification, twelve first coils37 are arranged. The twelve first coils 37 are arranged such that fourfirst coils 37 are adjacent to one another in the circumferentialdirection. Three first coil groups G1, each including the adjacent fourfirst coils 37 as one group, are arranged in the circumferentialdirection at regular intervals. The three first coil groups G1 areconstituted of a first UV coil group G1UV, a first VW coil group G1VW,and a first UW coil group G1UW.

The first UV coil group G1UV is constituted of two sets including a setof two first U-phase coils 37Ub and a set of two first V-phase coils37Va. The two first U-phase coils 37Ub are arranged adjacent to eachother in the circumferential direction, and are wound around the teeth34 in mutually opposite winding directions. The two first V-phase coils37Va are arranged adjacent to each other in the circumferentialdirection, and are wound around the teeth 34 in mutually oppositewinding directions. The first VW coil group G1VW is constituted of twosets including a set of two first V-phase coils 37Vb and a set of twofirst W-phase coils 37Wa. The two first V-phase coils 37Vb are arrangedadjacent to each other in the circumferential direction, and are woundaround the teeth 34 in mutually opposite winding directions. The twofirst W-phase coils 37Wa are arranged adjacent to each other in thecircumferential direction, and are wound around the teeth 34 in mutuallyopposite winding directions. The first UW coil group G1UW is constitutedof two sets including a set of two first U-phase coils 37Ua and a set oftwo first W-phase coils 37Wb. The two first U-phase coils 37Ua arearranged adjacent to each other in the circumferential direction, andare wound around the teeth 34 in mutually opposite winding directions.The two first W-phase coils 37Wb are arranged adjacent to each other inthe circumferential direction, and are wound around the teeth 34 inmutually opposite winding directions.

The pair of first U-phase coils 37Ua are connected with each other inseries, the pair of first V-phase coils 37Va are connected with eachother in series, the pair of first W-phase coils 37Wa are connected witheach other in series, the pair of first U-phase coils 37Ub are connectedwith each other in series, the pair of first V-phase coils 37Vb areconnected with each other in series, and the pair of first W-phase coils37Wb are connected with each other in series. Further, the pair of firstU-phase coils 37Ub are connected with the pair of first U-phase coils37Ua in series. The pair of first V-phase coils 37Vb are connected withthe pair of first V-phase coils 37Va in series. The pair of firstW-phase coils 37Wb are connected with the pair of first W-phase coils37Wa in series.

As illustrated in FIG. 8, in the second modification, twelve secondcoils 38 are arranged. The twelve second coils 38 are arranged such thatfour second coils 38 are adjacent to one another in the circumferentialdirection. Three second coil groups G2, each including the adjacent foursecond coils 38 as one group, are arranged in the circumferentialdirection at regular intervals. The three second coil groups G2 areconstituted of a second UV coil group G2UV, a second VW coil group G2VW,and a second UW coil group G2UW.

The second UV coil group G2UV is constituted of two sets including a setof two second U-phase coils 38Ub and a set of two second V-phase coils38Va. The two second U-phase coils 38Ub are arranged adjacent to eachother in the circumferential direction, and are wound around the teeth34 in mutually opposite winding directions. The two second V-phase coils38Va are arranged adjacent to each other in the circumferentialdirection, and are wound around the teeth 34 in mutually oppositewinding directions. The second VW coil group G2VW is constituted of twosets including a set of two second V-phase coils 38Vb and a set of twosecond W-phase coils 38Wa. The two second V-phase coils 38Vb arearranged adjacent to each other in the circumferential direction, andare wound around the teeth 34 in mutually opposite winding directions.The two second W-phase coils 38Wa are arranged adjacent to each other inthe circumferential direction, and are wound around the teeth 34 inmutually opposite winding directions. The second UW coil group G2UW isconstituted of two sets including a set of two second U-phase coils 38Uaand a set of two second W-phase coils 38Wb. The two second U-phase coils38Ua are arranged adjacent to each other in the circumferentialdirection, and are wound around the teeth 34 in mutually oppositewinding directions. The two second W-phase coils 38Wb are arrangedadjacent to each other in the circumferential direction, and are woundaround the teeth 34 in mutually opposite winding directions.

The pair of second U-phase coils 38Ua are connected with each other inseries, the pair of second V-phase coils 38Va are connected with eachother in series, the pair of second W-phase coils 38Wa are connectedwith each other in series, the pair of second U-phase coils 38Ub areconnected with each other in series, the pair of second V-phase coils38Vb are connected with each other in series, and the pair of secondW-phase coils 38Wb are connected with each other in series. Further, thepair of second U-phase coils 38Ub are connected with the pair of secondU-phase coils 38Ua in series. The pair of second V-phase coils 38Vb areconnected with the pair of second V-phase coils 38Va in series. The pairof second W-phase coils 38Wb are connected with the pair of secondW-phase coils 38Wa in series.

In the second modification, the pair of first coils 37 are excited toform magnetic fields in mutually opposite directions. The pair of secondcoils 38 are excited to form magnetic fields in mutually oppositedirections. Accordingly, the first coils 37 and the second coils 38 tobe excited in mutually opposite directions are alternately arranged inthe circumferential direction.

Therefore, in a motor 10 according to the second modification, thenumber of magnetic poles is larger than that of the first embodiment.Therefore, in the motor 10 according to the second modification,positions where torque is generated tend to be dispersed in thecircumferential direction. Therefore, the motor 10 according to thesecond modification can further suppress torque ripple.

(Third Modification)

FIG. 9 is a sectional view schematically illustrating a configuration ofa motor according to a third modification by cutting the motor in avirtual plane perpendicular to a central axis. In the thirdmodification, magnets 23 are embedded in a plurality of slots providedin a rotor yoke 22. The magnets 23 are arranged inside an outercircumferential surface of the rotor yoke 22 in a radial direction.Accordingly, a motor 10 according to the third modification can generatetorque to which reluctance torque is added.

Second Embodiment

FIG. 10 is a diagram for explaining waveforms of first U-phase andsecond U-phase currents to be supplied to a motor according to a secondembodiment. FIG. 11 is a diagram for explaining change amounts ofaverage torque and torque ripple with respect to a phase differencebetween a phase of a first motor drive current and a phase of a secondmotor drive current. A motor 10 and a motor control device 100 accordingto the second embodiment are the same as the motor 10 and the motorcontrol device 100 according to the first embodiment illustrated inFIGS. 1 to 6, but an operation of a phase difference adjusting unit 40Bof a control device 40 is different. Hereinafter, description will begiven with reference to FIGS. 1 to 6, and FIGS. 10 and 11 asappropriate. The same configuration elements as those described in thefirst embodiment are denoted with the same reference signs andoverlapping description is omitted.

As illustrated in FIG. 5, a main control unit 41 acquires steeringtorque T input to an input shaft 82 a from a torque sensor 91 a. Themain control unit 41 calculates a current value as a command value forrotating and driving a motor rotor 20 according to information acquiredfrom the torque sensor 91 a. A first coil system control unit 42calculates a first pulse width modulation signal with a predeterminedduty ratio, based on the command value from the main control unit 41.The first coil system control unit 42 transmits information of the firstpulse width modulation signal to a first phase adjusting unit 43. Asecond coil system control unit 44 calculates a second pulse widthmodulation signal with a predetermined duty ratio, based on the commandvalue from the main control unit 41. The second coil system control unit44 transmits information of the second pulse width modulation signal toa second phase adjusting unit 45.

In the second embodiment, the first phase adjusting unit 43 and thesecond phase adjusting unit 45 adjust a phase of a current to besupplied to second coil groups G2 such that the phase is advanced withrespect to a phase of a current to be supplied to first coil groups G1.The first phase adjusting unit 43 transmits information of the adjustedfirst pulse width modulation signal to a first gate drive circuit 51.The second phase adjusting unit 45 transmits information of the adjustedsecond pulse width modulation signal to a second gate drive circuit 53.

The first gate drive circuit 51 controls a first inverter 52 based onthe information of the first pulse width modulation signal acquired fromthe first phase adjusting unit 43. The first inverter 52 switches afield effect transistor on and off to generate three-phase alternatingcurrents including a first U phase, a first V phase, and a first Wphase, and having three-phase current values according to the duty ratioof the first pulse width modulation signal in the first gate drivecircuit 51. The three-phase alternating currents generated by the firstinverter 52 are sent to the motor 10 through three wires Lu1, Lv1, andLw1, and excite a plurality of first coils 37. The wire Lu1 sends afirst U-phase current to the motor 10. The wire Lv1 sends a firstV-phase current to the motor 10. The wire Lw1 sends a first W-phasecurrent to the motor 10.

The second gate drive circuit 53 controls a second inverter 54 based onthe information of the second pulse width modulation signal acquiredfrom the second phase adjusting unit 45. The second inverter 54 switchesa field effect transistor on and off to generate three-phase alternatingcurrents including a second U phase, a second V phase, and a second Wphase, and having three-phase current values according to the duty ratioof the second pulse width modulation signal in the second gate drivecircuit 53. The three-phase alternating currents generated by the secondinverter 54 are sent to the motor 10 through three wires Lu2, Lv2, andLw2, and excite a plurality of second coils 38. The wire Lu2 sends asecond U-phase current to the motor 10. The wire Lv2 sends a secondV-phase current to the motor 10. The wire Lw2 sends a second W-phasecurrent to the motor 10.

Similarly to the first embodiment, the first motor drive currents aresymmetrical three-phase alternating currents of the first U phase, thefirst V phase, and the first W phase, which have sine waves each shiftedby 120° in electrical angle. Further, the second motor drive currentsare symmetrical three-phase alternating currents of the second U phase,the second V phase, and the second W phase, which have sine waves eachshifted by 120° in electrical angle. Regarding the phase differencebetween the first motor drive currents and the second motor drivecurrents, a phase difference between the first U phase and the second Uphase is the same as a phase difference between the first V phase andthe second V phase, and a phase difference between the first W phase andthe second W phase. Therefore, the phase difference between the firstmotor drive currents and the second motor drive currents will bedescribed with reference to the phase difference between the first Uphase and the second U phase illustrated in FIG. 10.

As illustrated in FIG. 10, a phase difference β1 between a first U-phasecurrent Au1 of the first motor drive current and a reference phase is 0.The reference phase is a phase in which a phase difference between firstU-phase counter-electromotive force and a current of a phasecorresponding to the counter-electromotive force is 0°. The three firstcoil groups G1 are arranged in the circumferential direction of thestator core 31 at regular intervals. Therefore, when taking account ofonly the first coil groups G1, it can be considered that rotationaltorque proportional to the current to be supplied to the first coilgroups G1 is generated, and average torque becomes constant regardlessof a rotation angle of the motor rotor 20. However, a second U-phasecurrent Au2 of the second motor drive current is advanced with respectto a reference phase by a phase difference β2. The reference phase is aphase in which a phase difference between second U-phasecounter-electromotive force and a current of a phase corresponding tothe counter-electromotive force is 0. Therefore, as illustrated in FIG.11, average torque Ta decreases as the phase difference β2 becomeslarger than the reference phase, due to interaction between the firstcoil groups G1 and the second coil groups G2. By the way, the inventorshave found that the torque ripple Tr decreases as the phase differenceβ2 illustrated in FIG. 11 is advanced with respect to the referencephase, and the torque ripple Tr changes from decrease to increase at apredetermined extreme value, due to the interaction between the firstcoil groups G1 and the second coil groups G2. On the other hand, thetorque ripple Tr is expected to increase as the phase difference β2illustrated in FIG. 11 becomes smaller than the reference phase, due tothe interaction between the first coil groups G1 and the second coilgroups G2.

As illustrated in FIG. 11, when the phase difference β1 is 0, it is mostpreferable that the phase difference β2 is 10° in electrical angle.

As described above, the motor control device 100 according to the secondembodiment includes the motor 10, the control device 40, and a motordrive circuit 50. The motor 10 includes the motor rotor 20, the motorstator 30, and a plurality of coil groups that are divided into thefirst coil groups G1 and the second coil groups G2 of at least twosystems for each of three phases, and that excites the stator core 31with the three-phase alternating currents. The control device 40 outputsa current value as a command value for rotating and driving the motorrotor 20. The motor drive circuit 50 includes a first motor drivecircuit 50A and a second motor drive circuit 50B. The first motor drivecircuit 50A supplies the three-phase AC first motor drive current to thefirst coil groups G1 based on the command value described above, and thesecond motor drive circuit 50B supplies the three-phase AC second motordrive current to the second coil groups G2. The second motor drivecurrent has a phase difference from the first motor drive current suchthat the phase of the second motor drive current is advanced withrespect to the phase of the first motor drive current.

Accordingly, when two first coil group G1 and second coil group G2 to beexcited independently of each other are excited at the same time, torqueripple can be suppressed.

As described above, the control device 40 includes a control unit 40Athat calculates a pulse width modulation signal with a predeterminedduty ratio as a command value, and a phase difference adjusting unit40B. The phase difference adjusting unit 40B calculates a second pulsewidth modulation signal from a first pulse width modulation signal thatis the pulse width modulation signal with the predetermined duty ratio,such that the second pulse width modulation signal has the same dutyratio as the first pulse width modulation signal, and has a phasedifference (β2−β1) from the first pulse width modulation signal. Thephase difference adjusting unit 40B of the control device 40 adjusts thephase difference β2 in a range where the decreasing rate of the torqueripple is larger than the decreasing rate of the average torque, and themotor 10 is controlled to provide rotation with decreased torque rippleto the motor rotor 20. Further, the phase difference adjusting unit 40Bcan perform control to approximate the phase difference β2−β1) to 0 toincrease the average torque Ta, and increase the phase difference(β2−β1) to decrease the torque ripple Tr.

The first motor drive circuit 50A supplies the first motor drive currentto the first coil groups G1 by PWM control of the first pulse widthmodulation signal, and the second motor drive circuit 50B supplies thesecond motor drive current to the second coil groups G2 by PWM controlof the second pulse width modulation signal. Accordingly, the firstmotor drive circuit 50A and the second motor drive circuit 50B that areindependent from each other are provided, whereby redundancy isenhanced, and fail safety of the motor drive circuit 50 can be enhanced.

The above-described phase difference (β2−β1) does not exceed 45° inelectrical angle. Since the phase difference (β2−β1) does not exceed 45°in electrical angle, a decrease in the average torque Ta can besuppressed.

In the motor according to the second embodiment, output torque Ts isobtained by the following equation (1).

Ts=Tm+Tr  (1)

Here, Tm is torque by a magnetic flux φm of magnets 23 and Tr isreluctance torque. The reluctance torque Tr is obtained by the followingequation (2).

Tr=P(Lq−Ld)×Iq×Id  (2)

Here, P is the number of pole pairs of the magnets 23. Lq is q-axisinductance. Ld is d-axis inductance. Iq is a q-axis component of anarmature current. Id is a d-axis component of the armature current.

Typically, according to the equation (2), it can be seen that thereluctance torque Tr can be made large if the q-axis inductance Lq islarge and the d-axis inductance Ld is small. The torque Tm by themagnets 23 is determined by the following equation (3).

Tm=φm×Iq  (3)

Here, φm is a total amount of magnet magnetic flux of each pole pair.

As described above, the motor according to the second embodimentincludes the first coil groups G1 and the second coil groups G2.Therefore, the output torque Ts of the motor according to the secondembodiment can be considered separately as torque Tg1 by the first coilgroups G1 and torque Tg2 by the second coil groups G2. That is, theoutput torque Ts is obtained by the following equation (4).

Ts=Tg1+Tg2  (4)

The torque Tg1 is obtained by the following equation (5) when theformula (1) is applied.

Tg1=Tm1+Tr1  (5)

Here, Tm1 is magnet torque by the magnetic flux φm of the magnets 23with respect to the first coil groups G1. Tr1 is the reluctance torquewith respect to the first coil groups G1. Similarly, the torque Tg2 isobtained by the following equation (6) when the equation (1) is applied.

Tg2=Tm2+Tr2  (6)

Here, Tm2 is magnet torque by the magnetic flux φm of the magnets 23with respect to the second coil groups G2. Tr2 is the reluctance torquewith respect to the second coil groups G2.

FIG. 12 is a diagram illustrating vector relationships between anarmature magnetic flux of the first coil groups and an armature magneticflux of the second coil groups in a d axis and a q axis. The followingdescribes a case in which a phase difference 2δ is provided between anarmature magnetic flux mf1 of the first coil groups G1 and an armaturemagnetic flux mf2 of the second coil group G2 with respect to the q axisof a rotor magnetic pole, as illustrated in FIG. 12.

An addition average value of respective advance angles of the first coilgroups G1 and the second coil groups G2 with respect to the q axis ofthe rotor magnetic pole is β.

An advance angle of a rotating magnetic field of the first coil groupsG1 is (β−δ), based on the d axis of the rotor. Tm1 is obtained by thefollowing equation (7) where an amplitude value of an input current isIa.

Tm1=φm×Ia×cos(β−δ)  (7)

Similarly, Tr1 is obtained by the following equation (8).

Tr1=(Lq−Ld)×Ia ²×sin(β−δ)×cos(β−δ)  (8)

Tm2 is obtained by the following equation (9).

Tm2=φm×Ia×cos(β+δ)  (9)

Similarly, Tr2 is obtained by the following equation (10).

Tr2=(Lq−Ld)×Ia ²×sin(β+δ)×cos(β+δ)  (10)

β is from −90° to 90°, both inclusive. In the second embodiment, foreasy understanding, a case where β=0° is considered. In this case, anaddition value of a component of reluctance torque to the first coilgroups G1 and a component of the reluctance torque to the second coilgroups G2 is 0.

That is, when β=0 is assigned to the equations (8) and (10), thefollowing equation (11) holds.

Tr1+Tr2=0  (11)

According to the equation (11), by intentionally shifting the phases ofthe torque waveforms of the first coil groups G1 and the second coilgroups G2, the torque ripple components between the two groups of thefirst coil groups G1 and the second coil groups G2 are cancelled. As aresult, the torque ripple components can be suppressed even if thestator winding wires are not skewed, for example.

FIG. 13 is a schematic diagram of a vehicle on which the electric powersteering device including the motor according to the first or secondembodiment is mounted. As illustrated in FIG. 13, a vehicle 101 isprovided with the electric power steering device 80 including the motor10 according to the first or second embodiment. The vehicle 101 may beprovided with the motor 10 according to the first or second embodimentfor different use other than for the electric power steering device 80.

REFERENCE SIGNS LIST

-   -   10 MOTOR    -   11 HOUSING    -   11 a CYLINDRICAL HOUSING    -   11 d INNER CIRCUMFERENTIAL SURFACE    -   14 RESOLVER    -   20 MOTOR ROTOR    -   21 SHAFT    -   22 ROTOR YOKE    -   23 MAGNET    -   30 MOTOR STATOR    -   31 STATOR CORE    -   32 TOOTH TIP    -   33 BACK YOKE    -   34 TOOTH    -   37 FIRST COIL    -   37 a INSULATOR    -   37Ua and 37Ub FIRST U-PHASE COIL    -   37Va and 37Vb FIRST V-PHASE COIL    -   37Wa and 37Wb FIRST W-PHASE COIL    -   38 SECOND COIL    -   38Ua and 38Ub SECOND U-PHASE COIL    -   38Va and 38Vb SECOND V-PHASE COIL    -   38Wa and 38Wb SECOND W-PHASE COIL    -   40 CONTROL DEVICE    -   41 MAIN CONTROL UNIT    -   42 FIRST COIL SYSTEM CONTROL UNIT    -   43 FIRST PHASE ADJUSTING UNIT    -   44 SECOND COIL SYSTEM CONTROL UNIT    -   45 SECOND PHASE ADJUSTING UNIT    -   51 FIRST GATE DRIVE CIRCUIT    -   52 FIRST INVERTER    -   53 SECOND GATE DRIVE CIRCUIT    -   54 SECOND INVERTER    -   80 ELECTRIC POWER STEERING DEVICE    -   100 MOTOR CONTROL DEVICE    -   101 VEHICLE    -   G1 FIRST COIL GROUP    -   G1UV FIRST UV COIL GROUP    -   G1VW FIRST VW COIL GROUP    -   G1UW FIRST UW COIL GROUP    -   G2 SECOND COIL GROUP    -   G2UV SECOND UV COIL GROUP    -   G2VW SECOND VW COIL GROUP    -   G2UW SECOND UW COIL GROUP    -   Lu1, Lv1, Lw1, Lu2, Lv2, and Lw2 WIRE    -   Zr ROTATION CENTER

1. A motor control device comprising: a motor including: a motor rotor;a motor stator including a stator core that rotates the motor rotor; anda plurality of coil groups divided into a first coil group and a secondcoil group of at least two systems for each of three phases, andconfigured to excite the stator core by three-phase alternatingcurrents; and a motor drive circuit including: a control device thatoutputs a current value as a command value for rotating and driving themotor rotor; a first motor drive circuit that supplies a three-phase ACfirst motor drive current to the first coil group, based on the commandvalue; and a second motor drive circuit that supplies a three-phase ACsecond motor drive current having a phase difference from a phase of thefirst motor drive current, to the second coil group, wherein the phasedifference does not exceed 45° in electrical angle, the stator coreincludes an annular back yoke, and a plurality of teeth arranged side byside in a circumferential direction on an inner circumferential surfaceof the back yoke, when n is an integer, the 3n first coil groups arearranged in the circumferential direction of the stator core at regularintervals, each of the first coil groups being constituted of aplurality of first coils that are respectively wound, in a concentratedmanner, around the teeth arranged adjacent to one another, and that areexcited by a first inverter configured to generate three-phasealternating currents including a first U phase current, a first V phasecurrent, and a first W phase current, when n is an integer, the 3nsecond coil groups are arranged in the circumferential direction of thestator core at regular intervals, each of the second coil groups beingconstituted of a plurality of second coils that are respectively wound,in a concentrated manner, around the teeth adjacent to one another inpositions different from positions of the teeth around which the firstcoils are wound in a concentrated manner, and that are excited by asecond inverter configured to generate three-phase alternating currentsincluding a second U phase current, a second V phase current, and asecond W phase current, the first coils include a plurality of firstU-phase coils excited by the first U-phase current, a plurality of firstV-phase coils excited by the first V-phase current, and a plurality offirst W-phase coils excited by the first W-phase current, the secondcoils include a plurality of second U-phase coils excited by the secondU-phase current, a plurality of second V-phase coils excited by thesecond V-phase current, and a plurality of second W-phase coils excitedby the second W-phase current, the 3n first coil groups are constitutedof a first UV coil group that is constituted of only the first U-phasecoils and the first V-phase coils, a first VW coil group that isconstituted of only the first V-phase coils and the first W-phase coils,and a first UW coil group that is constituted of only the first U-phasecoils and the first W-phase coils, and the 3n second coil groups areconstituted of a second UV coil group that is constituted of only thesecond U-phase coils and the second V-phase coils, a second VW coilgroup that is constituted of only the second V-phase coils and thesecond W-phase coils, and a second UW coil group that is constituted ofonly the second U-phase coils and the second W-phase coils.
 2. The motorcontrol device according to claim 1, wherein the control deviceincludes: a control unit that calculates a pulse width modulation signalwith a predetermined duty ratio as the command value; and a phasedifference adjusting unit that calculates a second pulse widthmodulation signal from a first pulse width modulation signal that is thepulse width modulation signal with the predetermined duty ratio, suchthat the second pulse width modulation signal has the same duty ratio asthe first pulse width modulation signal, and has a phase difference fromthe first pulse width modulation signal.
 3. The motor control deviceaccording to claim 2, wherein the first motor drive circuit supplies thefirst motor drive current to the first coil group by PWM control of thefirst pulse width modulation signal, and the second motor drive circuitsupplies the second motor drive current to the second coil group by PWMcontrol of the second pulse width modulation signal.
 4. (canceled)
 5. Anelectric power steering device configured to obtain auxiliary steeringtorque by the motor of the motor control device according to claim
 1. 6.A vehicle on which the electric power steering device according to claim5 is mounted.